Cathode heating apparatus



Sept. 20, 1960 J. TOWNSEND 2,953,717

I CATHODE HEATING APPARATUS 7 Filed Feb. 19, 1959 2 Sheets-Shet 1 FIG. I. RT :LI

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(1 H H (l H (L U U H HUUU ()(I (l l) l) H (1H vvvv ! l CH I 1 cHc United States Patent CATHODE HEATING APPARATUS Jonathan Townsend, University City, Mo., assignor to Radiation Dynamics, Inc., New York, N.Y., a corporation of New York Filed Feb. 19, '1959, Ser. No. 794,388

24 Claims. (Cl. 31'5-97) This invention relates to a cathode heating apparatus and more particularly to voltage multiplication apparatus having means for heating the cathodes of high voltage rectifier tubes.

Among the several objects of this invention may be noted the provision of cathode heating apparatus which supplies electrical power to the cathodes of rectifier tubes without the need of auxiliary sources of power therefor; the provision of voltage multiplication apparatus in which power for heating the cathodes of the rectifier tubes thereof is made readily available directly to the cathodes and does not have to be furnished by additional devices such as auxiliary transformers; the provision of such cathode apparatus which is substantially independent of the frequency of the AC. potentials applied to said rectifier tubes; and the provision of voltage multiplication apparatus of the class described in which the power supplied to heat the rectifier tube cathodes is substantially independent of the level of the AC. potentials applied to the rectifier tubes. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

:Fig; l is a schematic circuit diagram of cathode heating apparatus of the present invention interconnected with a rectifier tube;

Figs. 2 and 3 are schematic circuit diagrams of two different embodiments of voltage multiplication apparatus of the present invention; and,

Figs. 410 are schematic circuit diagrams of additional alternative embodiments of cathode heating apparatus of the present invention interconnected with rectifier tubes.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawr ngs.

The supplying of power to heat the cathodes of rectifier tubes of voltage multiplication apparatus employing cascaded rectifier tubes has presented serious problems. Because there are high AC. and DC. potential differences between the various tubes, it has been necessary heretofore to employ individual batteries for each rectifier tube or to use isolation transformers built to withstand these high potential difierences. Neither arrangement is satisfactory inasmuch as batteries must be frequently renewed or recharged and isolation transformers of sufficient insulation and capacity to operate satisfactorily are bulky and expensive.

In accordance with the present invention voltage multiplication apparatus is provided in which no auxiliary source of power or isolation transformers are needed but power to heat the cathodes is made available right at the cathodes by novel cathode heating apparatus. The AC. charging or displacement current flowing through the capacitance constituted by the anode-cathode circuit of each of the rectifier tubes, due to the AC. potentials applied thereto, is utilized as the source of power for heating each of the rectifier tube cathodes. The appa-' ratus of the present invention is substantially independent of the frequency of these applied A.C. potentials and in certain of the more preferred embodiments the power supplied to each tube cathode is also substantially independent of the level of the AC. potentials applied to the rectifier tube anode-cathode circuit. I

-Referring now to Fig. l a cathode heating apparatus unit of the present invention is generally indicated at reference character CH. This unit is serially connected with the anode-cathode circuit of a rectifier tube RT across a source of high potential AC. power as indicated by wires L1 and L2. This is accomplished by interconnecting three electrical leads 1, 3 and 5 between heater unit CH and the cathode components RTC and RTF. Tube RT, which may be any of the conventonal types of tubes known to those skilled in this art (but is preferably of the high vacuum type), also includes an anode RTA, in addition to cathode RTC and filament RTF. Although tube RT is illustrated as an indirectly heated cathode type of tube, it is to be understood that directly heated cathodes are full equivalents and may be used, interchangeably (see Fig. 5) in carrying out the present" invention. It will be noted that cathode RTC and filament RTF are maintained at substantially the same electrical potential level by interconnecting the leads 1 and 3. j

One specific exemplary embodiment of the impedance transforming or heating unit CH is illustrated in Fig. 4. in which CH is a transformer having a magnetic circuit constituted by a ferromagnetic core CH-C with a first or primary winding W1 and a second or secondary winding W2. The core is preferably composed of ferrite but could be other ferro-rnagnetic material such as laminated silicon steel, etc. Upon application of an A.C. potential across L1L2 rectifier RT will conduct when its anode RTA is positive in relation to its cathode RTC and function as a half-wave rectifier. In addition the current con-' ducted by tube RT during the positive /2 cycles, there is a flow of AC. displacement or charging current across the capacitance constituted by the cathode RTC and anode RTA. The amount of displacement current which fiows both through RT and therefore winding W1 is a function of several parameters including that of the actual anodeoathode capacitance, the voltage level and frequency of the AC. potential applied across Ll-L2 and the impedance of any other components in the circuit including primary winding WI. The current flowing through W1 induces through transformer action an AC. potential across winding W2 which in turn supplies AC. power to filament RTF via wires 3 and 5 to heat cathode RTC- The turns ratio of WI and W2 is, of course, a function of the displacement current flowing through W1 and the' voltage and current requirements for energizing filament RTF. Unit CH can be manufactured quite economically and is very compact. It may be mounted directly on a base for the tube RT and needs no insulation inexcess of that necessary to withstand the relatively minor po tentials developed in the transformer itself.

An exemplary voltage multiplication apparatus of the present invention is shown in Fig. 2. High voltage cas- 1 7' second metallic electrode E2. These corona shields are connected at the electrical junctions between several series circuits (each comprising one tube RT and one heater unit CH). Thus, in effect by connecting corona shields CS2 and CS4 at alternate junctions relative to C81 and- CS3, the three rectifier-heater unit circuits are shunt-connected across electrodes E 1E2T via the interelectrode capacitances-inducted at CES, CESl; CES2 and- CES4. These interelectrode capacitances between E1- CS2 and El-CS4 (CESI and'CES3, respectively) and between E2CS1 and 132-653 (CBS and CES2, re-

spectively) serve to'capacitively'couple the A.C. poten-- tial across El-EZ to the rectifier and heater units. Al:-'

though these rectifier heater unit circuits are shunt-connected across the A.C. potential of-E1E2' through the' capacitances CES, CES1 CES2 and CES4, tubes RT are electrically connected in an anode-to-cathode. relationship between two" high voltage D.C. terminals TD1 and .TD2-, thereby effectively connecting in series the rectified DC. output potentials of each of rectifier tubes RT.

Upon application to metallic electrodesEl-EZofan A.C. potential, for example, in the order of 50,000'to.

charging. or displacement current is caused to flow through each of the first windings of the transformers, which induces a flow of current through the filament RTF. The cathodes of tubes RT are thereby heated and tubesRT will function as half-waverectifiers, the rectified, outputs of which are additively impressed across high voltage terminals TD1 and TD2. With twenty rectifier tubes RT, for example, connected as illustrated and anA.C. potential in theorder of 100 'kv. applied by E1--E2 to tubes RT, a DC. output potential in the order of 2 megavolts will be produced. The cathode heater transformer CH is not a resonant circuit and is there fore notsignificantly affected by moderate shifts in the tions is an important advantage of the present invention inasmuch as it is difiicult to economically maintain the frequency of the A.C. applied across E1E2 within a narrow range. Moreover, it is desirable to be able to vary this frequency and it would be quite disadvantageous if the filament heater power were seriously affected by such frequency shifts.

A second embodiment of voltage multiplication apparatus of the present invention is shown in Fig. 3, which is identical to the Fig. 2 embodiment except as tothe interconnection of the corona shields to the junctions between the several electrical circuits comprising a rectifier tube RT and a cathode heater CH. In Fig. 2 these electrical junctions are connected directly to the corona shields whereas in Fig. 3 these junctions are connected through winding W1 of heater units CH to the corona shields. An advantage of the Fig. 3 arrangement is that the winding W1 of each cathode heater unit CH which is connected between the electrical junctions (i.e., not the terminal units such as for example the unit CH connected to CS1) will carry the displacement currents flowing through two rectifiers RT, instead of merely one as is the case in the Fig. 2 embodiment. In the- Fig. 3 embodiment, therefore, the turns ratio between W1- and W2 may be reduced over that utilized in Fig. 2 for the same output potential of winding W2:

In many instances during operation of voltage multiplication apparatus of the present invention, itis desirable. tovary the A.C. potential across EI-EZswithout changing the potential applied by W2 to the filaments heating. apparatus-whichwill function to provide a-gsub- 4 stantially constant level of power to cathodes. In Fig. 5 heater unit CH includes a capacitor C and a resistor R series-connected in a loop circuit with said secondary winding W2. The core CHC is so constructed that the displacement current through winding W1 will saturate core CHC during most of the A.C. cycle. The voltage waveform of the secondary W2 is, therefore, in the shape of pulses of short time duration. As the area of these pulses is proportional to the saturation flux density, these pulse areas are independent of the'displacement current carried by winding W1. Resistor R and capacitor C constitute an integrating network to produce a voltage waveform atthe cathode-filament RTFl which has an r.m.s. value proportional to the area of the secondary winding pulses. Thus the power supplied to the cathode of RTFI is independent of the displacement current through W1. It will be noted that rectifier tube RTA of Fig. 5 is of the directly heated cathode type, i.e. one in which the cathode is constituted by a filament; Accordingly, wire 1 does not connect to an indirectly heated cathode, as in Fig. 4, but is simply connected'to one side of the filament RTF-l. It will be understood that this arrangement of connecting wire 1 to one side of the filament is the equivalentof connecting it to a center tap of winding W2.

The embodiment of Fig. 6' is' identical to that of Fig.- 5, with but two exceptions. The impedance constituted by resistor R of Fig. 5' is replaced by an inductor L- in Fig. 6,. and an indirectly heated type of cathode con-' struction (comprising both a cathode RTC and a filament RTF) is used in Fig. 6.

In the Figs. 7-9 embodiments regulation of heater poweris also provided.

tential in excess of a predetermined value will cause gas to ionize and the regulator to conduct) or the Zener diode type, or a varistor (such as a thyrite resistor) or any equivalent thereof. The Fig. 7 voltage regulator VR is connected in shunt across winding W1. In addition to providing regulation the use of a voltage regulator VR, particularly of the thyrite or glow-tube type, across the primary winding W1 also has the advantage of supplying protection against the possibility of high voltage sparkbreakdown at the high voltage terminal of a cascade rectifier. As these windings constitute high impedance elements to the spark which might otherwise develop damaging high voltages thereacross, theregulating element will provide a low impedance by-pass under such conditions.

The Fig. 8 embodiment illustrates two alternative arrangements for providing regulation. Either a varistor type of voltage regulator, such as a thyrite resistor T, is connected across the secondary winding W2, or a tertiary winding W3 with any other conventional voltage regulator, such as is indicated at VR, may be employed;

In Fig. 9 tertiary winding W3 and unit VR are connected in series in an electrical circuit which in turn is connected across windings W1 and W2. In each of the Figs. 7, 8 and 9 embodiments the windingsare tightly coupled by means of ferromagnetic core CHC and insure that the power supplied to the filament of the recti fier tube RT is substantially independent of the levelof the A.C. potential of E1-E2, as well as the frequency thereof.

The last illustrated embodiment, Fig. 10, is similar to that of Fig. 4 except that a current sensitive resistance element B (such as a barretter) is connected in series with the winding W2 and filament RTF, and an impedance, such as a thyrite resistor T1, is shunt-connected across winding W2. Component B functions to limit the current supplied to RT and thus assure regulation of the power supplied to the cathode of'RT'. The use of the:

parallel-connected thyrite varistor Tl -across secondary In these three embodiments a voltage regulator unit VR is'utilized. This unit VR may W2 in combination with element B further improves the regulation.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

-As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. Voltage multiplication apparatus comprising first and second metallic electrodes, a source of A.C. power connected to said electrodes, a plurality of first corona shields spaced from said first electrode, a plurality of second corona shields spaced from said second electrode, a plurality of rectifier tubes each having an anode and a cathode, means substantially independent of the frequency of said A.C. power source for electrically heating each of the rectifier tube cathodes comp-rising a transformer for each rectifier tube having a magnetic circuit including a ferromagnetic core and first and second windings thereon, and a plurality of electrical circuits each including a rectifier tube and the first winding of a transformer series-connected respectively between pairs of first and second corona shields whereby an A.C. potential is capacitively coupled from said electrodes through said corona shields to each of said electric circuits, each of said second windings being electrically connected to the cathode of a respective one of said rectifier tubes to heat it, said rectifier tubes being electrically connected in an anode-to-cathode relationship between two electrical terminals and adapted to supply a high DC. potential thereto.

2. Voltage multiplication apparatus comprising first and second metallic electrodes, a source of A.C. power connected to said electrodes, a plurality of first corona shields spaced from said first electrode, a plurality of second corona shields spaced from said second electrode, a plurality of rectifier tubes each having an anode and a cathode, means substantially independent of the frequency of said A.C. power source for electrically heating each of the rectifier tube cathodes comprising a transformer for each rectifier tube having a magnetic circuit including a ferromagnetic core and first and second windings thereon, each of said first windings interconnecting the anode of one rectifier tube with the cathode of the next rectifier tube at electrical junctions, each of said first and second corona shields respectively connected to alternate electrical junctions whereby an A.C. potential is capacitively coupled from said electrodes through said corona shields to each of said rectifier tubes, each of said second windings being electrically connected to the cathode of a respective rectifier tube to heat it, said rectifier tubes electrically connected in an anode-to-cathode relationship between two electrical terminals and adapted to supply a high DC. potential thereto.

3. Voltage multiplication apparatus comprising first and second metallic electrodes, a source of A.C. power connected to said electrodes, a plurality of first corona shields spaced from said first electrode, a plurality of second corona shields spaced from said second electrode, a plurality of rectifier tubes each having an anode and a cathode, said rectifier tubes being series-connected anodeto-cathode at electrical junctions between two electrical terminals and adapted to supply a high DC. potential thereto, and means substantially independent of the frequency of said A.C. power source for electrically heating each of the rectifier tube cathodes comprising a transformer for each rectifier unit having a magnetic circuit including a ferromagnetic core and first and second windings thereon, each of said first and second corona shields respectively connected to alternate electrical junctions through the first winding of one of said transformers, whereby an A.C. potential is capacitively coupled from 63 said electrodes through said corona shields to each of said rectifier tubes, each of said second windings being electrically connected to the cathode of a respective rechaving one end thereof connected to one side of a respec tive one of said filaments, said second winding being elecv trically connected across said filament.

5. Voltage multiplication apparatus as set forth in claim 3, in which each of said cathodes is indirectly heated by a respective filament, said second winding being electrically connected across said filament.

6. Voltage multiplication apparatus as set forth in claim 3, said core being composed of ferrite.

7. Voltage multiplication apparatus as set forth in claim 3 in which said cathodes each comprise a filament and which further includes an integrating network comprising a capacitor and an impedance serially connected in a loop circuit with said second winding, said first winding having one end thereof connected to said cathode and adapted to saturate said core during substantial portions of each cycle of the A.C. potential, said filament being electrically connected across said capacitor whereby the power supplied to heat said cathode is substantially independent of the level of said A.C. potential.

8. Voltage multiplication apparatus as set forth in claim 7, in which said impedance comprises a resistor.

9. Voltage multiplication apparatus as set forth in claim 3 which further includes a voltage regulator unit shunt-connected across said first winding whereby the power supplied to heat said cathode is substantially independent of the level of said A.C. potential.

10. Voltage multiplication apparatus as set forth in claim 3 which further includes a voltage regulator unit shunt-connected across one of said windings whereby the power supplied to heat said cathode is substantially independent of the level of said A.C. potential.

11. Voltage multiplication apparatus as set forth in claim 3 in which said transformer includes a third winding, and which further includes a voltage regulator unit connected across said third winding whereby the power supplied to said cathode is substantially independent of the level of said A.C. potential.

12. Voltage multiplication apparatus as set forth in claim 3 which further includes a third winding, a voltage regulator unit, and a circuit shunt-connected across said first and second windings, said circuit constituted by said regulator unit serially connected with said third winding whereby the power supplied to heat said cathode is substantially independent of the level of said A.C. potential.

13. Voltage multiplication apparatus as set forth in claim 3 which further incldes a current-sensitive resistor element and an impedance, said current-sensitive resistor element being serially connected in a circuit with said second winding and said cathode, said impedance being shunt-connected across said second winding, whereby the power supplied to heat said cathode is substantially independent of the level of said A.C. potential.

14. In voltage multiplication apparatus including a plurality of rectifier tubes each having an anode and a cathode and each adapted to have an A.C. potential impressed thereacross, said rectifier tubes electrically connected in an anode-cathode relationship between two electrical terminals and adapted to supply a high DC. potential thereto; means substantially independent of the frequency of said A.C. potentials for electrically heating the rectifier tube cathodes comprising a transformer for each rectifier unit having a magnetic circuit including a ferromagnetic core and first and second windings thereon, said first winding interconnecting the anode of one rectifier tube with the cathode of the next rectifier tube, said second winding electrically connected to said cathode to heat it, and a voltage regulator unit shunt-connected across one of said windings whereby the power supplied to heat said cathode is substantially independent of the level of said A.C. potential.

15. In voltage multiplication apparatus as set forth in claim 14, said cathodes being .directly heated cathodes constituted by filaments, each of said first winding having one end thereof connected to one side of the filament of the next rectifier tube, said second winding being electrically connected across said filament.

16. In voltage multiplication apparatus as set forth in claim 14, each of said cathodes being indirectly heated by a respective filament, said second winding being electrically connected across said filament.

17. In voltage multiplication apparatus as set forth in claim 14, said core being composed of ferrite.

18. In voltage multiplication apparatus including a plurality of rectifier tubes each having an anode and a cathode comprising a filament and each tube adapted to have an A.C. potential impressed thereacross, said rectifier tubes electrically connected in an anode-filament relationship between two electrical terminals and adapted to supply a high DC. potential thereto; means substantially independent of the frequency of said A.C. potentials for electrically heating the rectifier tube filament comprising a transformer for each rectifier unit having a magnetic circuit including a ferromagnetic core and first and second windings thereon, and an integrating network comprising a capacitor and an impedance serially connected with said secondary winding, said first winding interconnecting the anode of one rectifier tube with one side of the filament of the next rectifier tube and adapted to saturate said core during substantial portions of each cycle of the A.C. potential, said filament being electrically connected across said capacitor whereby the power sup: plied to heat said cathode is substantially independent of the level of said A.C. potentials.

19. In voltage multiplication apparatus as set forth in claim 18, said impedance comprising a resistor.

20. In voltage multiplication apparatus including a plurality of rectifier tubes each having an anode and a cathode and each adapted to have an A.C. potential impressed thereacross, said rectifier tubes electrically connected in an anode-cathode relationship between two electrical terminals and adapted to supply a high DC. potential thereto; means substantially independent of the frequency of said A.C. potentials for electrically heating the rectifier tube cathodes comprising a transformer for each rectifier unit having a magnetic circuit including a core and first and second windings thereon, said first winding interconnecting the anode of one rectifier tube with the cathode of the next rectifier tube, said second winding electrically connected to said cathode to heat it, and a voltage regulator unit shunt-connected across said first winding whereby the power supplied to heat said filament is substantially independent of the level of said A.C. potentials.

21. In voltage multiplication apparatus including a plurality of rectifier tubes each having an anode and a cathode and each adapted to have an A.C. potential impressed thereacross, said rectifier tubes electrically connected in an anode-cathode relationship between two electrical terminals and adapted to supply a high DC. potential thereto; means substantially independent of the frequency of said A.C. potentials for electrically heating the rectifier tube cathodes comprising a transformer for each rectifier unit having a magnetic circuit including a core and first and second windings thereon, said first winding interconnecting-the anode of one rectifier tube Q Q with the cathode of the next rectifier tube, said second winding electrically connected to said cathode to heat it, and a voltage regulator unit shunt-connected across said second winding whereby the power supplied to heat said filament is substantially independent of the level of said A.C. potentials.

22. In voltage multiplication apparatus including a plurality of rectifier tubes each having an anode and a cathode and each adapted to have an A.C. potential impressed thereacross, said rectifier tubes electrically connected in an anode-cathode relationship between two electrical terminals and adapted to supply a high DC. potential thereto; means substantially independent of the frequency of said A.C. potentials for electrically heating the rectifier tube cathodes comprising a transformer for each rectifier unit having a magnetic circuit including a core, and primary, secondary and tertiary windings thereon, said first winding interconnecting the anode of one rectifier tube with the cathode of the next rectifier tube, said secondary winding electrically connected to said cathode to heat it, and a voltage regulator unit connected across said tertiary winding whereby the power supplied to heat said filament is substantially independent of the level of said A.C. potentials.

23. In voltage multiplication apparatus including a plurality of rectifier tubes each having an anode and a cathode and each adapted to have an A.C. potential impressed thereacross, said rectifier tubes electrically connected in an anode-cathode relationship between two electrical terminals and adapted to supply a high DC. potential thereto; means substantially independent of the frequency of said A.C. potentials for electrically heating the rectifier tube cathodes comprising a transformer for each rectifier unit having a magnetic circuit including a core, and primary, secondary and tertiary windings thereon, said primary winding interconnecting the anode of one rectifier tube with the cathode of the next rectifier tube, said secondary winding electrically connected to said cathode to heat it, a voltage regulator unit, and a circuit shunt-connected across said secondary and primary windings constituted by said regulator unit serially connected with said tertiary winding whereby the power supplied to heat said filament is substantially independent of the level of said A.C. potentials.

24. In voltage multiplication apparatus including a plurality of rectifier tubes each having an anode and a filament and each adapted to have an A.C. potential impressed thereacross, said rectifier tubes electrically connected in an anode-filament relationship between two electrical terminals and adapted to supply a high DC. potential thereto; means substantially independent of the frequency of said A.C. potentials for electrically heating the rectifier tube filament comprising a transformer for 1 each rectifier unit having a magnetic circuit including a core and first and second windings thereon, said first winding interconnecting the anode of one rectifier tube with one side of the filament of the next rectifier tube, a current-sensitive resistor element, and an impedance, said second winding and said current-sensitive resistor element being serially connected with said filament, said impedance being shunt-connected across said second winding, whereby the power supplied to heat said filament is substantially independent of the level of said A.C. potentials.

Westendorp Dec. 31, 1935 Scha'de Mar. 2, 1937 

